In recent years, in order to improve the efficiency of an electric motor, a permanent magnet (PM) motor has been widely used. A neodymium magnet is a magnet having a higher efficiency than others but involves problems in terms of cost and the like because it contains a rare metal (rare earth).
As a magnet containing no rare metal, a magnet containing a ferrite magnet is generally used. However, in a radial air gap type electric motor having an air gap in the same direction as the rotating shaft, a ferrite magnet needs to be arranged along the rotation direction of the output shaft, and hence, in order to obtain the same performance as that of the neodymium magnet, it is necessary to increase the size of the electric motor to increase the volume of the ferrite magnet. That is, there is a problem in that the output and the size of an electric motor are in a trade-off relation.
As an electric motor which solves the relationship between the output and the size of the electric motor, an axial air gap type electric motor is known. The axial air gap type electric motor has a characteristic such that the thickness in the rotating shaft direction can be reduced, that is, the motor can be made to be flat, compared with the radial air gap type electric motors, such as an inner rotor type motor.
Patent Literature 1 discloses an axial air gap type electric motor in which a stator and a rotor plane-face each other via a predetermined air gap widening in the radial direction of the rotating shaft. Specifically, the axial air gap type electric motor includes: a stator formed by arranging a plurality of stator cores in a ring shape about the rotating shaft; and two rotors each facing each of the both end surfaces of the stator in the rotating shaft direction. The core member of the stator is formed by an iron core, an insulator (bobbin), and a coil. The iron core is a laminated iron core having a substantially trapezoidal-shaped cross-section formed by laminating metal plate-like members in the radial direction of the rotating shaft.